1. Field of the Invention
This invention relates to a mounting and/or positioning mechanism for a light source in a luminaire (i.e. amp unit), particularly, but not exclusively, for application in theatre, studio or other entertainment lighting.
2. Description of the Prior Art
In, for example, theatre lighting it is often desired to produce a shaped patch of light so as to give the impression of light through a window, for instance. For this purpose, a gate and shutter assembly is provided within the luminaire housing. The gate comprises a plate mounted transverse to the beam from the luminaire. A plurality of shutters (usually at least four) are provided each comprising a blade within the plane of the gate and a handle projecting out from the lamp housing through a slot. By manipulating the handle for each blade, the operator can swivel the blade angularly and also push the blade in and out of the aperture within the gate plate.
The gate plate is disposed between the light source (for example an incandescent bulb or lamp) and a projecting lens system, and these components are positioned such that the gate plate and shutters form a virtual object for the lens system, so that the light spot from the luminaire is the same shape as the shape defined between the shutter blades. For some theatrical effects, it is desirable that the intensity distribution within the spot of light is uniform, whereas for other effects a distribution with a higher intensity in the centre of the spot, falling off towards the edge may be preferred. The distribution of the light across the gate is dictated by the relative position of the light source to the parabolic or ellipsoidal reflector within which it is located, and in many lamps this position is variable by means of a positioning mechanism.
Incandescent lamps (and other types of light source) need replacing at fairly frequent intervals. They may need to be replaced whilst the luminaire is sited on the ceiling of a theatre or studio, for instance. To avoid having to remove and dismantle the entire housing and optical arrangement, the light source is often arranged to be removable through the rear of the lamp, together with its mounting block and power cable whilst the luminaire remains in situ. After changing the light source, the light source and its mounting block are then remounted in the luminaire.
In one known type of luminaire, the axial (i.e. longitudinal) focus position adjusting mechanism comprises a slot cut in the rear of the luminaire housing, and a threaded locking knob projecting through the slot inserted into the mounting of the light source. The slot is open at the rear end of the lamp housing. When it is desired to remove the light source, the knob is loosened and the mounting and knob together with the light source are withdrawn from the rear of the housing. The reverse process is carried out on reinserting the mounting. Then the focus is adjusted as desired by sliding the knob along the slot, and tightening the knob when the desired position is reached. This method of adjusting the focus is quick and easy to use, and is therefore often adopted. One example of such a construction is in the Lekolite (registered trademark) spotlight available from Strand Lighting Limited; another is in the 5/50 series spotlights available from Lee Colortran International.
However, this arrangement does have the disadvantage that when it is necessary to change the light source in use, the previous focus position is lost and the focus must be readjusted, which is inconvenient during a live performance and involves additional labour costs.